RECOVERY OF GLASS WASTES IN A CONTINUOUS KILN

Projektdetails

Gesamtkosten:

EU-Beitrag:

Koordiniert in:

Thema(en):

Finanzierungsprogramm:

DEM - Demonstration contracts

Ziel

To recover energy in manual glass manufacturing by reprocessing glass scrap in a continuous kiln. Expected energy savings are 3600 Nm3/day of natural gas. A recovery of ca. 3000 kg/d of glass is also foreseen.Measurements were taken with the dual aim of: (i) determining the potential energy saving(ii) determining the quantity of raw material saved by recovering the waste glass.These two aspects are related since saving energy is possible because the new installation uses high-temperature waste glass. In order to calculate the potential energy saving, it is necessary to make a comparison between the new installation and a conventional foundry used as a reference. Measurements taken at an actual conventional foundry showed that, in energy terms, the most important factor is the ratio between the production of glass (net of waste) and energy consumption. This ratio for conventional foundry is 1.925 kg/Nm3. With the new installation, the theoretical average ratio between glass production and energy consumption is around 4.05 kg/Nm3.If waste is taken into account, the figure is considerably lower and drops to an average of 2.39 kg/Nm3.By inverting these ratios we obtain the followingfigures:0.519 Nm3 of gas/kg of glass in a conventional furnace0.418 Nm3 of gas/kg of glass in the new installation.For a glass production of 2 470 kg/day the fuel saving works out at 249.5 Nm3 of natural gas a day, which over 285 working days a year is a saving of 60.5 toe a year. Apart from saving energy, the plant makes it possible to recycle a large quantity of the raw material. A comparison of the relevant figures with the investment, operating and maintenance costs required to build and operate this plant shows that this demonstration project is not yet economically worthwhile.In fact it will take nearly 17 years to see a return on investment. If the plant were built on an industrial scale instead of a demonstration scale this payback time could be reduced, but not sufficiently to make this project an economic proposition at the moment.There are basically two reasons for this: the low cost ot natural gas at the moment and the quality of glass required for subsequent production of goods which is very high in the case of IVV.However, if there is a significant increase in the price of natural gas it is possible that some manufacturers of lower quality glass products may find the project of interest since it would reduce their levels of waste and might therefore make their plants more competitive.In the specific case of IVV, it is the energy saving aspect which is of most interest since the scheme made it possible to eliminate three crucible kilns. For the same level of glass production, the new continuous kiln has a consumption of 147.7 toe/year. This represents a saving of 361 toe/year which is certainly appreciable, even though the original estimates have not been achieved. In fact, it was originally hoped to replace six crucible kilns and although this would have been possible in terms of quantity, it is not if waste is taken into account.The project foresees modifications to the existing glass manufacturing plant : replacement of some crucible kilns by a new continuous kiln with a capacity of 3 t/day of glass waste; automatic feeding equipment and two tanks.Glass is recovered in the first tank and maintained at a sufficiently high temperature to keep it fluid. The glass is transferred to the second tank whence it is taken for manufacture.The glass production consists of a continuous kiln which operates 24 hours a day 285 days a year and 14 crucible kilns which operate 8 hours a day during the same 285-day period.Average production of the continuous kiln is 11 000 kg of glass per 24-hour period. The continuous kiln is fired by natural gas with a lower calorific value of 8 500 kcal/Nm3. Gas consumption is 4 000 Nm3 a day or 1 140 000 Nm3/year.It has been observed that some 30 % of the glass produced by the continuous kiln is wasted since the initial and final parts of the "gob" being processed are thrown away.This is absolutely essential in order to maintain the high quality glass product. This means that 3 300 kg of glass is discarded every day of which, in the old configuration, only 1 100 kg were recycled so as not to impair the quality of the glass significantly.Although there are 14 crucible kilns in all, only 10 of them operate at any one time for 8 hours a day 285 days a year. Each crucible kiln produces some 500 kg of glass a day for a daily consumption of 700 Nm3 of natural gas.The recycling part of the plant consists of a six-axis robot which takes the glass waste out of the continuous kiln and puts it into the new kiln nearby.A robot has to be used to transfer the glass fron the continuous kiln to the new kiln quickly in order to reduce cooling of the "gob" to a minimum. Because the operation must be carried out very quickly, only a robot of sufficient power, speed and flexibility can carry out this task, particularly since glass comes out of the continuous kiln at temperatures in excess of 1 300 C.The new kiln is a hearth kiln.